The present invention relates to carburetors for internal combustion engines and in particular to fuel metering and dispersion systems for controlling the air-fuel mixture in a carburetor.
Carburetor metering systems have generally been employed for the purpose of maintaining a constant air fuel ratio over a broad range of throttle positions. For example, in Monosmith, et al., Pat. No. 1,974,286 an air valve is linked to a fuel flow valve so that an increase in air flow causes a proportionate increase in the amount of fuel injected. However, this carburetor does not use a spool valve for regulating fuel injection into the carburetor mixing chamber nor is it capable of precise fuel metering. In addition, the Monosmith patent does not provide a structure wherein the fuel is injected into the airflow at the point of maximum air flow velocity, i.e., at the narrowest point or throat in the air-fuel mixing passageway. Monosmith, et al., does incorporate a dashpot-like device for enriching the air-fuel ratio on rapid acceleration or cold starting.
The fuel metering system disclosed in Fish Pat. No. 2,236,595, has a fixed venturi area and a throttle plate pivotally mounted in the air-fuel mixing passageway of the carburetor. However, the fuel discharge openings are on a pivotal throttle member which makes it impossible for the fuel to be dispersed at the narrowest portion of the air-fuel mixing passageway at all throttle positions as in the present invention. In addition, fuel metering is accomplished by a pivotal arm attached to the throttle plate which extends into the fuel chamber. A passageway from the throttle plate apertures through the radial arm terminates at the end of the arm in spaced varying relationship to the carburetor wall so that as the arm is rotated the orifice area increases to permit greater fuel flow. In such a carburetor, the rate of fuel delivery may be matched to the position of the throttle plate. However, this carburetor suffers from the disadvantage that the venturi area is fixed (at a given throttle setting) and thus the air flow is not responsive to engine demands.
A carburetor having an adjustable fuel metering means similar to that disclosed in the Fish patent is also disclosed in Hammerschmidt et al., Pat. No. 3,291,464.
Other fuel metering systems are disclosed in Obermeyer, Jr. Pat. No. 3,284,062 and Mick Pat. No. 3,342,462. Each of these fuel metering systems provide a link between the air valve and a fuel flow control mechanism so that the greater the opening of the air valve the greater will be the amount of fuel injected into the air-fuel mixing passageway. While each of these devices has certain advantages, each fails to provide the precision fuel metering necessary to effect optimal air fuel mixing over a wide range of operating conditions thus resulting in sub-optimal fuel economy and higher than necessary pollution. Additionally, the injection of fuel does not occur at the location of maximum air velocity, namely at the narrowest point or throat of the air-fuel passageway over the entire range of throttle openings as in the present invention.
In an effort to solve these problems and provide a more precision fuel metering system, the inventor herein previously invented a carburetor fully described in U.S. Pat. No. 3,752,451, which provides a fuel spray bar in a mixing passageway between a pair of venturi plates in the upstream portion of the mixing passageway of the carburetor and a pair of throttle plates in the downstream portion of the mixing passageway. Fuel is supplied to the fuel spray bar in the mixing passageway by a pivotal fuel dispersing pickup arm, which moves over a calibrated metering ramp in the fuel chamber to form a variable fuel metering clearance between the metering ramp in the fuel dispersing pickup arm. The movable venturi plates and the pickup arm are linked to provide for concurrent pivotal movement of the two. The ramp in the fuel chamber which is variably spaced from the pickup arm opening, cooperated with the pickup arm opening to provide a non-linear variable fuel metering clearance so as to maintain the air fuel mixture ratio in the mixing chamber substantially constant. However, the fuel is again injected above the carburetor throat (between the throttle plates) in an area of lesser air velocity.
Unlike any of the above referenced carburetor and systems for fuel metering the present invention provides a carburetor where the fuel dispersion orifices are located transversely opposite the edge of a pair of throttle plates which is the narrowest point along the air-fuel mixing passageway for all throttle positions. This assures that the fuel will always be injected into the air stream through the carburetor at the point of maximum air flow velocity.
In addition, the present invention includes a variable radius metering arm which variably opens and closes a ball valve in response to the opening of a pair of venturi plates to allow fuel to pass from a reservoir into a fuel dispersion assembly. The contour of the cam surface of the variable radius metering cam against which the ball valve assembly presses is selected empirically over a range of operating conditions whereby the amount of fuel metered to the fuel dispersion assembly is optimized at each of a number of throttle positions with the contour of the variable radius metering arm being derived therefrom. In addition, the steady state closure position of the ball valve can be adjusted by incorporation of a valve adjustment sleeve, which is movable upwardly or downwardly in response to the turning of a valve closure adjustment shaft, to thereby increase or decrease the steady state ball valve opening. Such an arrangement allows for substantially greater precision without the necessity of a large number of precision parts.
The present invention also provides a unique on-off flow controlled valve which allows fuel to flow into the reservoir only upon initial pivoting of one of the venturi plates. Only slight initial rotation of one of the venturi plates is required to actuate the on-off fuel flow control valve to the fully opened position to allow fuel to flow into the reservoir.
In accordance with another further advantage of the present invention, float valves and the like are unnecessary because the system incorporates and takes advantage of the fuel pressure to additionally control dispersion of the fuel into the air-fuel mixing passageway. More specifically, the fuel entering the carburetor initially enters through a pressure regulator which maintains the pressure of fuel at a constant pressure of about four pounds per square inch. Thus, fuel in the system and particularly in the reservoir will be under pressure. Thereafter, the fuel is metered to a fuel dispersion assembly which includes a fuel dispersion bar with a flow passageway extending tranversely across the chamber of the carburetor. The fuel dispersion bar has a cylindrical flow passageway with a plurality of fuel dispersion slits which extend radially out from the flow passageway exiting into the air-fuel mixing passageway in a direction transverse to the direction of air flow through the carburetor. A spool valve extends through the flow passageway to variably open and close the plurality of fuel dispersion slits to vary the amount of fuel dispersed into the air-fuel mixing passageway in response to a fuel flow diaphragm which moves in response to the volume and pressure of the fuel flowing through the carburetor.
The throttle plates are positioned to close against the lateral or side facing apexes of the dispersion bar so that the velocity of the air passing through the carburetor will be greatest at the point of fuel injection into the air-fuel mixing passageway.
The fuel discharged from the fuel dispersion bar is discharged at a constant pressure by incorporating a fuel pressure control assembly. Specifically, the fuel passing through the fuel metering rod is applied against one side of a diaphragm where the other side of the diaphragm has a compression spring which applies a desired force so that as the volume of fuel flow into the dispersion bar increases the diaphragm will be deflected to open the spool valve and allow more fuel to be discharged through the dispersion slits so that the fuel pressure will be maintained at a constant value. On the other hand, if the flow of fuel decreases, the diaphragm deflects in the opposite direction, thereby closing the dispersion slits. The spool valve therefore enables the carburetor in accordance with the invention to more precisely discharge fuel into the mixing chamber.
Tests with a carburetor manufactured in accordance with the invention have been conducted and have demonstrated that substantially higher air-fuel ratios are possible to achieve the same performance which conventional carburetors yield, that fuel economy is greatly increased, and that undesired pollution is greatly decreased.